It's really frustrating that it can be so unclear. I've talked to people about this that are gluten free and have actually had them laugh at the idea that gluten or dairy,etc are not always openly called such on an ingredient label. However, people can change their diets and wonder why they are not feeling better, and this can be exactly why: They truly haven't taken the gluten or dairy out of their diet by missing these things in products. Cecelia's Marketplace Guide is a lifesaver because they do the guess work for you. All of the products in there are gluten and dairy free (the gluten and casein guide). It's not all inclusive, so there may be gluten and dairy free products out there that are not included in the manual. However, everything in there is guaranteed to be gluten and dairy free. This is especially helpful on a vacation where there are stores (for example "Publix") that might not be a chain where you usually live. I have found a lot of Safeway brand products that I can eat which is especially helpful when traveling to Canada as they have Safeway stores on the West Coast.
From my personal experience. . . for awhile I was feeling really sick and didn't know why. I had been on a bouillon kick (don't ask me why!) and was putting it in everything. The ingredients didn't say anything about wheat at all. So, I called the company just to make sure. The gal seemed shocked that I would ask such a silly question and told me for sure there was wheat in the product. Much to my shagrin, I took it out of my daily meals and really improved.
So if all else fails, do feel free to call the company. I am always able to find someone at a company that knows if there is gluten or dairy in a product. The other thing is celiac.com is a great resource for those that are gluten free. You can search a product name in the box and there is usually someone who has already contacted the company about a product and shares what they found with the forum. This can be incredibly helpful.